Conventionally, application of an EGR system to a supercharged internal combustion engine is known as disclosed in, for example, Patent Literature 1. The EGR system constitutes a low pressure (LP) circuit EGR system. The LP circuit EGR system recirculates a low-pressure exhaust gas to the internal combustion engine by connecting an exhaust passage on a downstream side of an exhaust turbine, and an intake passage on an upstream side of a compressor. In accordance with the LP circuit EGR system, an EGR gas can be introduced into an intake gas that has not been boosted yet, a large amount of EGR gas can be recirculated to the internal combustion engine.
On the other hand, the LP circuit EGR system has a problem that the EGR gas is cooled to generate condensed water when the EGR gas joins the intake gas. When the condensed water is generated, erosion is caused to occur in an impeller of the compressor. In this regard, the EGR system of Patent Literature 1 includes an EGR heater that heats the EGR gas to a predetermined temperature in an EGR passage. When the EGR heater is operated, a temperature of the EGR gas can be increased before the EGR gas joins the intake gas. Therefore, the occurrence of the erosion can be suppressed by reducing an amount of the condensed water on the upstream side of the compressor.
Patent Literature 1: Japanese Patent Application Publication No. 2009-174444
However, the above EGR heater is for heating only, and when the EGR heater is installed, problems of a cost increase and ensuring of a space are unavoidable. Also, since a pressure loss in the above EGR heater is increased, an advantage of the LP circuit EGR system that the large amount of EGR gas can be recirculated to the internal combustion engine is possibly impaired.
The present invention has been made in view of the above problems. That is, an object is to provide an exhaust gas recirculation system for an internal combustion engine that can suppress occurrence of erosion in a compressor impeller by using an existing system.